1. Field of the Invention
The present invention relates to an image reading apparatus and image reading system comprising the image reading apparatus. More particularly, the present invention relates to an image reading apparatus which can be suitably carried in a portable electronic device as well as favorably read a detectable object image.
2. Description of the Related Art
In recent years, the continuous global proliferation of Information Technology Equipment (ITE) and other compact electronic devices, such as cellular phones, Personal Digital Assistants (PDAs), etc. has been truly remarkable. Furthermore, there is a growing public demand for these electronic digital devices to be outfitted with credit card payment processing cryptographic functions for processing electronic money or e-money and digital cash payments. In order to maintain security on individual account and eliminate security vulnerabilities, an electronic device outfitted with a personal authentication function which identifies and authenticates an individual user is needed. This type of personal authentication requires a device comprising an image reading apparatus that reads a detectable object image, for example, a fingerprint, etc.
Several types of image reading apparatus for reading detectable object images, such as a fingerprint, etc. are known which for example use an electrostatic capacity reading type configuration or an optical type configuration of a Charged-Coupled Device (CCD), Complementary Metal Oxide Semiconductor (CMOS) sensors, etc. The electrostatic capacity type configuration read an image of a detectable object by detecting an electrostatic capacity difference based on a detectable object (finger) and an electrical potential difference generated between detection sensors. Also, some reading apparatus have an optical type configuration which read light and dark information of a detectable object via an optical system, for example, a prism, a mirror, etc.
As for an electrostatic capacity type configuration mentioned above, although the detection sensor area where a detectable object is placed for reading an object image can be formed in a thin and lightweight construction, this type of image reading apparatus is highly susceptible to static electricity damage of the detection sensor by a static electricity charge from a detectable object.
Conversely, although a thin and lightweight construction in an optical configuration is problematic when the optical system is intervened between a detectable object and the photosensors, this type of image reading apparatus is resistant to static electricity damage of the photosensors by a static electricity charge from a detectable object and has an advantage in that fingerprint reading response speed is also relatively faster.
However, since CCD or CMOS sensors are abundantly in use as photosensors which are situated above a semiconductor substrate and these sensors contain an opaque layer, an electronic device comprising such an image reading apparatus must be installed in a different location besides the image display section. For this reason, when considering the size of an image reading apparatus in such a configuration which requires an area of sufficient size for reading detectable object images, such as fingerprints, etc., there is a persistent problem that the overall size of the electronic device will increase. Therefore, in order to control enlargement in the size of the electronic device, the size of an image reading apparatus must be smaller. In that case, it becomes troublesome to satisfactorily read detectable object images, such as fingerprints, etc. Thus, there is a drawback in that a structurally stable personal authentication device has not yet been technologically advanced.